In a wireless communications network employing beamforming techniques, the quality of downlink signals received by a mobile station (MS) from a base transceiver station (BTS) is determined by beamforming weighting vectors used for transmitting signals on a downlink channel, which beamforming weight vectors are created from the covariance matrix of the downlink channel. However, lack of information about channel coefficients of the downlink channel makes it difficult for the BTS to obtain optimal downlink beamforming weighting vectors, especially in a fast fading environment employing frequency division duplex (FDD) or time division duplex (TDD) techniques.
A downlink beamforming weighting vector can be computed using a downlink channel covariance matrix, which is obtained from an uplink channel covariance matrix. Since the BTS transmits signals to an MS using the downlink beamforming weighting vector, it needs the MS to provide constant feedback on the performance of the network. The feedback received from the MS helps the BTS to decide how to modify the downlink beamforming weighting vectors in order to maintain or enhance the performance of the wireless network.
In a conventional wireless network, the BTS applies a beamforming weighting vector to signals to be transmitted via multiple BTS antennas to the antennas of the MS before transmitting signals to the MS. The BTS continues transmitting signals with the same beamforming weighting vector. Since channel conditions are not static, the same weight vector may not consistently yield the same level of network performance.
As such, what is desired is a method for improving the performance of the wireless network utilizing a set of beamforming weighting vectors according to the feedback received from an MS.